1. Field of the Invention
The present invention relates to a fuel cell including an electrolyte electrode assembly, separators sandwiching the electrolyte electrode assembly, and seal members. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte interposed between the electrodes. Further, the present invention relates to a fuel cell stack formed by stacking the fuel cells.
2. Description of the Related Art
Generally, a solid polymer fuel cell employs a polymer ion exchange membrane as a solid polymer electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. The solid polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly. Each of the anode and the cathode is made of electrode catalyst and porous carbon. The membrane electrode assembly is sandwiched between separators (bipolar plates) to form the fuel cell.
In the fuel cell, a fuel gas (reactant gas) such as a gas chiefly containing hydrogen (hereinafter also referred to as the hydrogen-containing gas) is supplied to the anode. An oxidizing gas (reactant gas) such as a gas chiefly containing oxygen (hereinafter also referred to as the oxygen-containing gas) is supplied to the cathode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating a DC electrical energy.
Generally, several tens to hundreds of unit cells are stacked together to form a stack of the fuel cell. These unit cells need to be in alignment with each other accurately. In order to achieve the accurate positioning of the unit cells, typically, a knock pin is inserted in each of positioning holes formed in the unit cells. When a large number of the unit cells are stacked together, the operation of inserting the knock pins into the holes of the unit cells is laborious, and the fuel cell cannot be assembled efficiently. Positional displacement between components may occur undesirably, and the desired sealing performance may not be achieved.
In an attempt to address the problem, Japanese Laid-Open Patent Publication No. 2000-12067 discloses a solid polymer electrolyte fuel cell 1 as shown in FIG. 15. The fuel cell 1 includes a unit cell 2 and separators 3a, 3b sandwiching the unit cell 2. The unit cell 2 includes a solid polymer electrolyte membrane 2a, an anode 2b provided on one surface of the solid polymer electrolyte membrane 2a, and a cathode 2c provided on the other surface of the solid polymer electrolyte membrane 2a. 
Holes 4 extend through the fuel cell 1 in a stacking direction of the fuel cell 1 for inserting holding pins 6. The separator 3b has openings 5 for inserting snap rings 7. The holding pin 6 has a snap ring attachment groove 6a. The holding pin 6 is inserted into the hole 4, the snap ring 7 is inserted into the opening 5, and the snap ring 7 is fitted to the snap ring attachment groove 6a. At one end of the holding pin 6, a chamfered tip 6b is formed. At the other end of the holding pin 6, a hole 6c for inserting the tip 6b of another holding pin 6 is formed.
As described above, in the system of the fuel cell 1, the holding pin 6 is inserted into the hole 4, and the snap ring 7 is inserted into the opening 5. The snap ring 7 is fitted to the snap ring attachment groove 6a of the holding pin 6 for tightening the fuel cell 1.
Thus, the tip 6b of the holding pin 6 projecting from the outer surface of the separator 3b is fitted to the hole 6c of another holding pin 6 which tightens another fuel cell 1. In this manner, the adjacent fuel cells 1 are stacked in alignment with each other.
In the conventional technique, a plurality of the holding pins 6 need to be inserted into the holes 4 for each of the unit cells 2. Further, the snap ring 7 needs to be fitted to the snap attachment groove 6a of each of the holding pins 6. Thus, when a large number of unit cells 2 are stacked together, operation of assembling the holding pin 6 and the snap ring 7 is considerably laborious, and cannot be performed efficiently.
When the fuel cell 1 is assembled, the tip 6b of the holding pin 6 projects from the outer surface of the separator 3b. Thus, electrical leakage may occur from the tip 6b of the holding pin 6.